There is a need in the microwave food industry for inserts useful in microwavable containers that are more efficient in removing excess grease and moisture from food during cooking in a microwave oven.
A wide variety of inserts useful in microwavable food containers have been developed to improve the quality of food cooked in a microwave oven. For instance, it is known to place a liquid absorbent pad within a package for absorbing food byproducts such as moisture and grease exuded from food during cooking in a microwave oven (U.S. Pat. No. 4,873,101). Such pads must not only provide sufficient capacity for the quantity of food byproducts produced during cooking, but must withstand the elevated temperatures required to adequately cook the precooked or cured foods discussed above without degradation.
Similarly, U.S. Pat. Nos. 4,954,356 and 4,857,342 disclose a microwavable package for storing and cooking a food product including an absorbent bed enclosed within a sealed plastic sleeve. Also, U.S. Pat. No. 4,950,524 discloses a bacon pad made of liquid absorbent wood fibers. U.S. Pat. No. 4,786,513 discloses a package of sliced bacon containing an absorbent blotter means.
U.S. Pat. No. 4,873,101 discloses a package of food containing a substantial amount of water and solidified grease that can be cooked within the package in a microwave oven. The package further comprises a pad adjacent the food comprising microwave radiation transparent generally hydrophobic liquid grease absorbing materials that are capable of holding the amount of grease in the food when it is melted.
U.S. Pat. No. 5,094,869 describes a food degreaser which uses a layer of absorbent fiber on the inside of a wicking material envelope.
Other known grease absorbing pads have been found to be useful, such as the insulating product which is sold under the trade designation "Thinsulate" by Minnesota Mining and Manufacturing Company, St. Paul, Minn., in densities of 40, 100 and 200 grams/m.sup.2 and absorbs or holds about 15, 16 and 91/2 times its own weight of grease, respectively; the products sold under the trade designation "Oil Sorbent" and "Insorb Industrial Wipe" by Minnesota Mining and Manufacturing Company, St. Paul, Minn., which have densities of about 36 and 70 grams/m.sup.2, respectively, and absorb or hold about 14 and 8 times their own weight in grease, respectively.
For example, in U.S. Pat. No. 4,865,854 pads of blown microfibers are described which are constructed of a composition comprising a blend containing substantially equal parts by weight of polypropylene and poly 4-methylpentene-1 (PMP), 0.16 cm (0.062 inch) in thickness and thermally embossed on both sides with a 0.40 cm (0.156 inch) hexagonal pattern and having densities in the range of nine and one half (91/2) to six (6) times their weight in grease.
However, conventional absorbent pads absorb both water and various greases from the food. This is undesirable in that if part of the absorbent capacity of the pad is occupied by moisture, insufficient capacity may remain for grease.
It is also desirable in many cases for water exuded from a food in the form of steam during cooking to be maintained in close proximity to the food as to evenly distribute heat within the package and to reduce the cooking for the food. An additional problem occurs during extended storage and transportation of a package containing a food having substantial amounts of water and grease. A pad that absorbs water as well as grease will tend to gradually absorb water from the food. Thus, a subsequent measurement will show that the weight of the food has been reduced compared to the weight at the time the package was sealed.
Therefore, there is a need in the art to find new microwavable inserts which show improvement over the standard microwavable inserts that are useful in microwavable food containers. This is true especially in the area of optimization of grease or moisture transport depending on whether the food is prone to greasiness or a combination thereof.
Also disclosed in the art are microwavable inserts comprising a plastic film with a thin metal coating or "metallized film". The metallized film is generally used in direct contact with a food item. Part of the microwave energy passes through to heat the food item dielectrically while part is converted to heat by the metallized film to sear the coating in contact therewith. U.S. Pat. No. 4,703,148 describes this particular art in detail.
Also known in the art are microwavable inserts having two layers, the first of which is a top layer consisting of an absorbent layer made from fibers, the second of which is a metallized susceptor layer. These inserts are known as "Wavealites".
In copending application Ser. No. 736,267, continuation-in-part of U.S. Ser. No. 333,651, now abandoned, fibers are disclosed which are capable of spontaneously transporting water and other hydrophilic fluids on their surfaces. Additionally, other fibers of sufficient chemical composition and geometry are capable of spontaneously transporting n-decane and other hydrophobic fluids. Such fibers will be referred to herein as "spontaneously transportable fibers" or, alternatively, "spontaneously wettable fibers." We have unexpectedly discovered that use of fibers of sufficiently complex geometry, especially spontaneously transportable fibers, when incorporated into microwavable cooking structures, results in improved wetting and aids in aqueous and/or nonaqueous transport of fluids released during microwave cooking with appropriate surface energetics.